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The .455 Webley was based on the older .450 Adams and .476 Enfield cartridges (although neither of these cartridges provided a parent case for the .455 Webley) which had a case diameter of .476in, a feature that meant that the .455 Webley would be used for a longer period of time as well as quickly replace the older cartridges as firearms chambered for those cartridges would need no adjustment to accept the .455 Webley.

The .455 Webley was designed to fire a .455 diameter soft lead bullet. However the intervention of the Hague Conventions of 1899 and 1907 meant that the British Armed Forces could not use soft lead bullets as these could deform when they entered the human body. However, the bullet needed to deform to allow it to engage with the rifling in the barrel, otherwise it would tumble and greatly reduce accuracy. After 1907, the use of soft-lead declined in the .455 Webley, with various lead alloys being used instead.

The .455 Webley has been developed over its service life, with major changes occuring as a result of the Hague Conventions of 1899 and 1907. Each version had its own markings and reason for development.

The Mk I of the .455 Webley, officially becoming the standard calibre of British sidearms in 1891, was the first version of the .455 Webley. Using 265 grains (17g) of blackpowder to propel a soft-lead round nose bullet, the Mk I would be replaced by a more efficient version in 1897 when experiments with cordite as a propellant showed that a shorter case was more efficient. Its case length is a bit longer than the later versions of the round at .848 inches.

The Mk II, adopted in 1897, was identical to the Mk I bar two significant features. As mentioned above, the Mk II used cordite to propel the same round nosed, soft lead bullet but was also made shorter, with cordite burning more efficiently in shorter cartridge lengths.

Known more memorably as the "Manstopper" bullet, the Mk III of the .455 Webley featured a soft lead hollow point bullet, designed to be used by police and colonial forces. Introduced in 1899, the Manstopper was almost immediately banned from military use by the terms of the 1899 Hague Convention, due to the fact that it was designed to deform (as a result of a hemi-spherical hollow cavity which was designed to allow the bullet to deform), with the Mk II re-entering service in 1900.

The Mk IV .455 Webley was an attempt to put the Mk III into service without violating the terms of the Hague Convention. Instead of a hollow point bullet, the Mk IV used a flat-nosed soft-lead bullet. The Mk IV was also designed to improve upon the Mk II in terms of efficiency.

The Mk V .455 Webley was the first of the .455 Webley cartridges to feature a new harder lead alloy, rather than the soft lead of old. Introduced in 1914 the Mk V would fail to stay the distance, being replaced by the Mk II (in the same year) as stocks of the Mk II remained and proved to be more effective with the Webley Revolver during the First World War.

The Mk VI .455 Webley was the first .455 Webley to fully comply to the Hague Convention, albeit 22 years after the 1907 meeting. With a copper Full Metal Jacket and a harder lead, round nose bullet the .455 Webley would be used during the Second World War by British Forces. Two propellants were used with the Mk VI, with a choice of either nitrocellulose (a more powerful propellant that had seen greater use in the 1920's and 30's), marked "VIz", or more traditional cordite, marked "VI".

The Auto Mk I is a version of the .455 Webley designed specifically to be used in semi-automatic pistols such as the M1911 in 1913. The cartridge was semi-rimmed to be more efficent in the semi-automatic pistols being primarily used by the Royal Navy.

The .455 Webley is a deliberately low to moderate power cartridge, designed so that the heavy frame Webley Revolver, combined with a lower power cartridge, will produce little to no recoil meaning a greater rate of fire and better accuracy. The calibre size of .455 means that the .455 Webley has superb stopping power and penetration with little recoil produced.

Bullet Weight / Type

Velocity

Energy

265gr (17g) / FMJ

700 ft/s (210 m/s)

289 ft/lbf (392J)

265gr (17g) / Mk I

600 ft/s (180 m/s)

212 ft/lbf (287J)

265gr (17g) / Auto Mk I

750 ft/s (230 m/s)

337 ft/lbf (457J)

265gr (17g) / Mk II

600 ft/s (180 m/s)

220 ft/lbf (300J)

The various different versions of the .455 Webley all produced roughly the same muzzle velocities and energy figures, even with changes in propellent amounts, with the figures shown above representing the major changes in design.

The .455 Webley would be used by the British Army for as long as the Webley Revolver remained in service. In its 76-year service life, the .455 Webley would be manufactured by a variety of companies before virtually disappearing entirely. As a result, any firearm chambered in .455 require no license to own (in the UK), as the .455 calibre has been deemed obsolete and therefore difficult to obtain. However in Italy and the United States the .455 Webley Mk II remains in production with Fiocchi and Hornady respectively.

The low power of the .455 Webley made it a popular target shooting round, particularly in practical shooting, as very little recoil is produced with the heavy frame Webley Revolver. The .455 Webley also became a popular round to be tuned to greater pressures, as the Webley could cope with much higher pressures than the standard .455 Webley could produce.